With the recent progress toward higher integration of semiconductor devices, the circuit interconnects are becoming finer and the interconnect spacing is becoming narrower. In the manufacturing of a semiconductor device, films of a variety of materials are repeatedly formed on a substrate, such as a wafer, to form a multi-layer structure. A technique of planarizing the surface of the substrate is important for the formation of the multi-layer structure. Substrate processing apparatuses for performing chemical mechanical polishing (CMP) are widely used as a means to planarize the surface of the substrate.
Such a substrate processing apparatus generally includes a polishing table to which a polishing pad is attached, a polishing head for holding a wafer, and a polishing liquid nozzle for supplying a polishing liquid onto the polishing pad. While rotating the polishing head and the polishing table individually and supplying the polishing liquid from the polishing liquid nozzle onto the polishing pad, the wafer is pressed against the polishing pad by means of the polishing head, thereby polishing the wafer.
Unwanted residues remain on the polished wafer. In order to remove such residues from the wafer, the substrate processing apparatus includes a plurality of cleaning units for cleaning the wafer, and a plurality of drying units for drying the cleaned wafer. FIG. 12 is a schematic view showing layout of cleaning units and drying units provided in a conventional substrate processing apparatus. As shown in FIG. 12, the substrate processing apparatus is provided with two cleaning lanes: an upper cleaning lane and a lower cleaning lane. In the upper cleaning lane, a wafer is transported in the order of: an upper cleaning unit 152, an upper cleaning unit 154, and an upper drying unit 156, while in the lower cleaning lane, a wafer is transported in the order of: a lower cleaning unit 160, a lower cleaning unit 162, and a lower drying unit 164. Two wafers are cleaned and dried in parallel in the upper and lower cleaning lanes.
In the upper cleaning unit 152, the upper cleaning unit 154, the lower cleaning unit 160 and the lower cleaning unit 162, a wafer is cleaned with a cleaning member, such as a brash or a sponge, which is rubbed against the wafer while a liquid chemical is being supplied to front and back surfaces of the wafer, followed by rinsing of the wafer with pure water. In the upper drying unit 156 and the lower drying unit 164, the front surface of the wafer is rinsed with pure water, and then the wafer is dried by an IPA vapor (gas mixture of isopropyl alcohol and N2 gas) which is supplied to the front surface of the wafer.
The pure water is supplied to the cleaning units 152, 154, 160, 162 and the drying units 156, 164 for processing of a wafer. Therefore, as shown in FIG. 12, a pure-water supply pipe 300 extending from a factory pure-water line, which is one of factory utilities, is coupled to each of the cleaning units 152, 154, 160, 162 and the drying units 156, 164. The pure-water supply pipe 300 is equipped with a main pure-water valve 301.
Bacteria may grow in the cleaning units 152, 154, 160, 162 and the drying units 156, 164. Living or dead bacteria may be conveyed, along with pure water, to a wafer, thus contaminating the wafer. It is, therefore, conventional practice upon the growth of bacteria to inject a hydrogen peroxide solution into the pure-water supply pipe 300 to kill bacteria, and subsequently inject pure water into the pure-water supply pipe 300 to clean (flush) the interior of the pure-water supply pipe 300.
The pure water is distributed from the single pure-water supply pipe 300 to the cleaning units 152, 154, 160, 162 and the drying units 156, 164. When bacteria grow in one of the units 152, 154, 160, 162, 156, 164 in such a pure-water supply system, a hydrogen peroxide solution should necessarily be introduced into the entirety of the pure-water supply pipe 300. As a result, both of the upper cleaning lane and the lower cleaning lane become unavailable for cleaning of wafers. It may take several hours to complete cleaning of the pipe using the hydrogen peroxide solution. This causes the problem of long downtime during which processing of a wafer is stopped.